<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
        margin: 0;
        padding: 0;
        }
        .content{
            margin-left: 20px;
            width: 203px;
        }
        input{
            outline: none;
            border: 0;
            border-bottom: 1px solid #000000;
        }
        .btns{
            display: flex;
            flex-wrap: wrap;
        }
        .btns>section{
            width: 45px;
            height: 45px;
            border-radius: 22.5px;
            background-color: #a8a8a8;
            text-align: center;
            line-height: 45px;
            justify-content: space-between;
        }
    </style>
</head>
<body>
<div class="content">
    <section>算式：<input type="text"></section>
    <section>结果：<input type="text"></section>
    <div class="btns">
        <section>C</section>
        <section>CE</section>
        <section></section>
        <section></section>
        <section>1</section>
        <section>2</section>
        <section>3</section>
        <section>+</section>
        <section>4</section>
        <section>5</section>
        <section>6</section>
        <section>-</section>
        <section>7</section>
        <section>8</section>
        <section>9</section>
        <section>*</section>
        <section>/</section>
        <section>0</section>
        <section>.</section>
        <section>=</section>

    </div>
</div>


</body>
</html>